Electromagnetic field radiation detector having audible and visual indicators for detecting frequencies within the range of five hertz to four hundred kilohertz

Abstract

A system for detecting the presence of a magnetic field emanating from a video display terminal (VDT) in which a current induced through a sensing element is first amplified by a high gain amplifier stage having a very broad low band frequency response curve then rectified by a precision rectifier to convert the AC signal induced through the sensing element to DC current. The DC current is used as one input to a comparator, the other input being set by means of a potentiometer to provide flexibility in setting a threshold input voltage differential representative of a harmful magnetic field radiation level. The output of the threshold comparator triggers a driver which is connected to a battery powered solenoid. The solenoid actuates an indicator flag in the presence of a magnetic field which exceeds the threshold magnetic radiation level. To conserve battery energy, the energized solenoid also functions as a relay to break electrical contact between itself and the batteries simultaneously with actuating the flag indicator. An alternative embodiment invention replaces the pickup coil of the preferred embodiment with a Hall effect current sensor to sense the strength of the magnetic field. In a third embodiment of the invention a radiation detector is produced having astable multi-vibrators 250 and 256 which respectively produce an audible and visual warning signal.

What is claimed is: 
     
       1. A radiation detector adapted to detect and provide a warning of a presence of radiation having a frequency of about 5 hertz to about 400,000 hertz, said radiation detector comprising: coil means for sensing said radiation and for producing an alternating electrical current signal when said radiation is sensed;   amplifier means, coupled to said coil means, for amplifying said alternating electrical current signal only when said frequency of the sensed radiation is less than about 2,000 hertz, thereby producing an amplified signal;   first rectification means, coupled to said coil means, for rectifying said alternating electrical current signal only when said frequency of the sensed radiation is greater than about 2,000 hertz, thereby for producing a first direct current signal;   second rectification means, coupled to said amplifier means, for rectifying said amplified signal, thereby producing a second direct current signal;   summing means, coupled to said first and second rectification measure, for summing said first and second direct current signals, thereby producing a summed signal;   comparator means, coupled to said summing means, for comparing said summed signal to predetermined value and for producing a comparison output signal only when said summed signal exceeds said predetermined value;   first multi-vibrator means, coupled to said comparator means, for selectively producing a visual alarm signal only when said comparison output signal is produced by said comparator means; and   second multi-vibrator means, coupled to said first multi-vibrator means, for selectively producing an audible alarm signal a predetermined time after said visual alarm signal is produced, thereby cooperating with said first multi-vibrator means to provide a warning of said presence of said radiation.   
     
     
       2. The radiation detector of claim 1 further comprising power supply means for supplying electrical power to said amplifier means, comparator means, and to said first and second multi-vibrator means. 
     
     
       3. The radiation detector of claim 2, wherein said power supply means comprises a first battery, and a second battery coupled in parallel to said first battery.